But Dr Tom Marshall, a public health expert, said natural variations in readings meant high blood pressure could be over-diagnosed.

Dr Marshall studied the blood pressure findings of more than 13,000 adults whose blood pressure had been taken each year over three years as part of a larger study into cardiac disease risk factors.

He then analysed the data to calculate how many were truly hypertensive.

He found that, of 36 men aged 16 to 34 who had been classified as needing treatment, only 11 really needed treatment.

Of 19 women, only five actually needed to be on medication to lower their blood pressure.

'No symptoms'

Dr Marshall said young adults were at low risk of heart disease and there was little benefit from treatment.

He said hypertension in young adults should be diagnosed with caution by taking the
average of many blood pressure measurements or even using a higher threshold than is used now.

He added: "In adults under 35 clinicians should diagnose hypertension with caution.

"Blood pressure measurement is useful mainly in people with specific indications or coronary risk factors."

Belinda Linden, of the British Heart Foundation, said: "Treatment for high blood pressure is generally not considered until someone has been found to have a consistently raised blood pressure on three consecutive occasions over a number of months. This should ensure that treatment is not started unnecessarily.

"High blood pressure often has no obvious symptoms. Measurement is the only way to ensure appropriate treatment is given and the risk of coronary heart disease in later life is avoided.

"Hypertension is more prevalent in older people, but with the growing problem of obesity and inactivity, it is possible that high blood pressure will increasingly affect younger people.

"For that reason, it is important to remain vigilant in checking blood pressure levels."